Measuring Entanglement Entropy in a Quantum Many-Body System
Fig. 1: Bipartite entanglement and partial measurements*. [Reprinted by permission from Macmillan Publishers Ltd: Nature ©2015]
Entanglement is one of the most intriguing features of quantum mechanics. It describes non-local correlations between quantum objects, and is at the heart of quantum information sciences. Entanglement is now being studied in diverse fields ranging from condensed matter to quantum gravity. However, measuring entanglement remains a challenge. This is especially so in systems of interacting delocalized particles, for which a direct experimental measurement of spatial entanglement has been elusive.
Prof. Markus Greiner's group has developed a way to directly access entanglement in in such a system of itinerant particles using quantum interference of many-body twins. Making use of their single-site-resolved control of ultracold bosonic atoms in optical lattices, the team prepared two identical copies of a many-body state and interfered them. This enabled the scientists to directly measure quantum purity, Rényi entanglement entropy, and mutual information. These experiments pave the way for using entanglement to characterize quantum phases and dynamics of strongly correlated many-body systems.
*see Rajibul Islam, Ruichao Ma, Philipp M. Preiss, M. Eric Tai, Alexander Lukin, Matthew Rispoli & Markus Greiner, "Measuring entanglement entropy in a quantum many-body system," Nature 528(03 December 2015) doi:10.1038/nature15750. Also read Steven Rolston's Nature News & Views article "Quantum physics: Getting the measure of entanglement" (ibid.) describing the research done by the Greiner team and its significance to advancing our understanding of non-equilibrium systems.